This invention relates to a process and an apparatus for etching glass, and, in particular, transparent glass, in order to reduce its reflectance. Glass products are etched for a variety of reasons today, but many of these reasons arise from the need for reducing the visible specular reflectivity of the glass. Use of low specular reflectance or "non-glare" glass has become almost a necessity in face plates for television screens and monitors for computers. It is also in high demand for use in picture framing glass to reduce the glare created by the reflection of light incident upon the surface of glass covering works of art, photographs, posters and the like.
One common means of reducing the reflectivity of generally large or rectangular sheets of glass has been to etch such glass sheets as generally described in U.S. Pat. No. 3,374,130 to Junge. In the etching process, a glass sheet is suspended from a rack and then dipped, for a predetermined time period, in an etching bath containing a solution of hydrofluoric acid and ammonium bi-fluoride. In some baths, a glycol and/or sugar may be added to control the viscosity of the bath and produce a finer etch. The temperature and mixture of components in the bath must be carefully controlled to achieve a good quality etch. The etching solution creates small irregularities in the surface of the otherwise smooth glass which scatter the reflected light so as to reduce glare. Variations of the etching process are taught by various patents, including U.S. Pat. No. 3,374,141 issued to Pittsburgh Plate Glass Company. Other methods of reducing glare include the application of coatings of metal oxides, such as aluminum oxide compositions by deposition to glass surfaces. Such coatings have a refractive index between that of the glass and the air and thereby act to decrease reflectivity. The coating process is taught in U.S. Pat. No. 2,338,233 issued in 1944 to G. L. Dimmick, among others.
Even with the greatest possible control over the etching process, including the ingredients of the bath, the creation of surface irregularities on both sides of the glass sheet by the acid etch will reduce the resolution and the optical clarity of the glass which is etched. In addition, processes of coating by deposition or otherwise require multiple layers of materials and substantial time and expense to produce. Thus, manufacturing non-glare glass using these methods may not be economically justifiable depending upon the use of the resulting products, as for example, in picture framing glass.
While there have been attempts to improve resolution by etching or treating only one side of a sheet of glass, this has generally been done by applying a protective paste by hand to the side which is not to be etched. The paste will not react with the etch bath and prevents the bath from contacting the underlying glass surface. However, after dipping in the etching bath, the paste must be removed from the glass surface, thereby substantially slowing the entire manufacturing process. Non-glare surfaces have also been created by casting procedures, which are entirely different from the etching procedure described in this application. Such procedures and the deposition of coatings, as described above, all involve substantial preparation, time and expense and are, therefore, not desirable for use i manufacturing non-glare picture framing glass or even screens for certain televisions and video monitors.
It is an object of the present invention to provide an economical, highly automated apparatus for etching generally, but not limited to, rectangular sheets of glass on a single side.
It is a further object of this invention to provide an apparatus for etching at least two sheets of glass simultaneously and thereby improving manufacturing efficiency and economy.
One more object of the invention is to provide a process for reducing the glare from a glass surface while improving the resolution of the glass treated by the process.
It is still another object of the invention to provide a process for introducing multiple sheets of glass into an etching solution and etching at least one surface of each sheet of glass simultaneously to reduce glare.
It is still a further object of this invention to provide a process and apparatus in which more than one sheet of glass may be simultaneously etched, but on one side only, in order to reduce glare while improving resolution.
It is yet another object of this invention to provide a process and apparatus by which sheets of glass to be etched are sealed in face to face relationship, to allow etching of such sheets of glass on opposite outer faces thereof in an etching bath.
Yet another object of this invention is to produce a sheet of glass or glass article which has been selectively etched on one side only by an immersion process in order to reduce glare while improving resolution.